Fuel cell batteries are a type of device which converts chemical energy into electric energy. As shown in FIG. 1, a currently available fuel cell battery generally comprises a chamber unit (1), an anode entrance (2) connected to chamber unit (1), an anode exit (3), a cathode entrance (4) and a cathode exit (5). Anode entrance (2) is connected to a fuel source (22) through a duct (21). A valve (26) is installed on duct (21). A valve (20) is installed at anode exit (3). Cathode entrance (4) is connected to an oxidant source (24) through a duct (23). Chamber unit (1) contains an anode (6), a cathode (7), and a proton-exchange membrane (8) located between anode (6) and cathode (7).
Anode (6) is a type of gaseous diffusion electrode, with its supporting material generally made of electric conductive carbon fiber or carbon fabric. A catalyst is located between anode (6) and proton-exchange membrane (8) to catalyze the anode chemical reaction. Such anode catalyst is generally platinum powder, alloy powder containing platinum, platinum loaded on a carrier, or alloy powder containing platinum loaded on a carrier. Said alloy containing platinum also has one or more of the following including ruthenium, stannum, indium, osmium, and rhenium. Said carrier, such as active carbon, is electrically conductive and has relatively high surface area. On the external side of the anode is the current collector which can be made of graphite material or metal material.
Cathode (7) is also a type of gaseous diffusion electrode, with an identical structure as in the anode. The difference is that the catalyst between cathode (7) and proton-exchange membrane (8) catalyzes the cathode chemical reaction. Such cathode catalyst is generally platinum powder, or platinum powder loaded on a carrier. On the external side of the cathode is a current collector, which can be made of graphite material or metal material.
The proton-exchange membrane (8) is a type of semi-permeable membrane that is air-water-tight but not water-air-tight. The membrane conducts protons, and it can also prevent mixing the catalyst and the fuel which can cause an explosion.
In the following examples, the fuel is methanol and hydrogen, and the oxidant is air or oxygen. The fuel enters the anode side of chamber unit (1) through anode entrance (2), passing through anode (6) and leading to a chemical reaction.
When the fuel is methanol, the chemical reaction of anode (6) is:CH3OH+H2O→CO2+6H++6e  (1)
When the fuel is hydrogen gas, the chemical reaction of anode (6) is:3H2→6H++6e  (2)
The generated carbon dioxide and the unreacted fuel are discharged through anode exit (3).
Meanwhile, the following chemical reactions happen at cathode (7): 3/2O2+6H++6e→3H2O,  (3)
The chemical reactions (1) and (3), and the reactions (2) and (3) of the individual electrodes respectively lead to the following general reactions:CH3OH+ 3/2O2→CO2+2H2O  (4)3H2+ 3/2O2→3H2O  (5)
The above reactions at anode (6) and cathode (7) create a voltage difference between the two electrodes. The electrons generated by anode (6) are captured by the cathode after moving through the current collector and the external conductor located on the external side of the anode. The protons generated by anode (6) will be directly passed on to cathode (7) through the proton membrane, creating an electric current.
Not only can the fuel of said fuel cell be methanol and hydrogen gas, but it can also be other organic fuel. For example, said organic fuel can be selected from one or more of the following including alcoholic fluid, aqueous ether, and organic acid fluid. Alternatively, the organic fuel can be selected from one or more of the following including alcoholic fluid solution and acid fluid solution. The preferred selection has one or more of the following including methanol, ethanol, formic acid (or methanoic acid), and ethylether. Alternatively, the selection can have one or more of the following including methanol solution, ethanol solution, and formic acid (or methanoic acid) solution.
Said fuel cell using organic fuel has the advantages such as minimized pollution, a low noise level, a simple structure, being easy to carry, and a wide variety of fuel sources which are easy to obtain. Also, because the organic fuel is liquid, it has a high energy ratio. In terms of storage, there is no need to use, for example, a pressurized container, making it easy to carry. Meanwhile, compared to the inflammable hydrogen gas which is prone to explosion, organic fuel is reliably safe.
Although fuel cells using organic fuel have the above mentioned advantages, there are also certain disadvantages. A major one is that the platinum catalyst is not effective with organic fuel. In the process of catalyzing the oxidization of the organic fuel, carbon monoxide is generated as a byproduct. The carbon monoxide byproduct mixes with the platinum in the catalyst and forms a stable coordination compound, poisoning the catalyst. Therefore, compared to a cell using hydrogen fuel, the above mentioned cell using organic fuel has a very low density of electrode power output in a unit area. Taking said cell using methanol as an example, based on reported data, the density of power output in a unit area of a cell using hydrogen is more than ten (10) times that of said cell using methanol. To achieve the same power output, a cell using organic fuel must have an active area several times that of a cell using hydrogen gas. Consequently, the use of costly metal in the catalyst, such as platinum, also has to be several times more. Therefore, when organic fuel is used in the cell, the manufacturing cost of the fuel cell increases significantly.
Typical electronic product have similar power requirement from batteries, and the batteries generally operates in cyclic pulses. Taking the cell phone as an example, during the long periods in the standby mode, the cell phone operates on low power and its requirement for the cell's power output remains low. However, during the short period of telephone communication, the cell phone operates on high power and the requirement for the battery's power output will be high. Between those two operating conditions, there is a difference of roughly ten (10) times in power output requirement.
Using hydrogen gas as fuel, a fuel cell can have a very high density of power output in a unit area. The reason is that the catalyst containing platinum is highly effective in hydrogen gas. Therefore, theoretically a cell using hydrogen gas can meet the dual requirements of both a long standby and a high power output during the short period of telephone communication. However, the disadvantage of using hydrogen gas as fuel lies in the highly inflammable nature of hydrogen gas which is prone to explosion. So far, there is no ideal way of storing hydrogen gas. To achieve a long standby period on a cell phone, large amount of hydrogen needs to be carried, creating potential safety hazards and limiting the transportation options of the battery user.
If organic fuel is used, a fuel cell must have a much larger size and a much larger cell area to meet the requirement of high power output during a short time. That will increase the manufacturing cost of the fuel cell and its bulkiness.